It is desirable to have a thermal printer in which it is easy to accurately load the dye donor ribbon. It is desirable to make the printer as easy to use as practical while being cost effective in the manufacturing process. Some thermal printers have a disposable dye donor cartridge mounted in the printer to hold the dye donor supply and take-up spools and offer convenience of use because it is relatively easy to insert and remove the cartridge. This is especially true in instances where the cartridge is keyed to be insertable with only one orientation. While cartridges offer convenience, they are expensive and discarded after one use. Unfortunately, attempts to make cartridges reusable to conserve resources have failed because it is difficult to rewind dye donor in a cartridge at the point of use.
To eliminate the problems associated with cartridges, some printers have configurations that mount the donor spools in the print engine without the benefit of a cartridge, while other printers mount the spool in the printer door, again without cartridges. Where spools are used without cartridges, there are also problems that arise. Space is always a consideration and there is not always sufficient room for all hands to manipulate the spools, regardless of whether the spools are full or empty. A spool can be mispositioned on the drive elements and therefore completely inoperative, or may cause annoying printing errors.
Failure to correctly orient the supply and take-up spools creates a situation wherein the printer will not function properly, if at all. Correct loading requires having the supply and take-up spools in their proper places as well as having the donor supply spool oriented correctly end for end. Incorrect end for end orientation causes the web to traverse an incorrect path through the printer, if it traverses a path at all. With an improperly loaded dye donor web, it is very difficult, if not impossible, to achieve exact color registration and produce a quality image with undesirable artifacts.
While a careful and skillful operator can study the spools and the spool receiving mechanism and achieve correct insertion of the supply and take-up spools, doing so is burdensome, even for a skilled operator. An operator does not want to read lengthy or complicated instructions or observe burdensome or annoying practices just to ready a machine for use, and typically has more than one machine to operate and desires convenience so that having to refer to manuals or read instructions is quite a burden. An operator wants to simply drop the donor web into place, especially where doing so is an occasional and unscheduled chore. Accordingly, it will be appreciated that it would be highly desirable to have an apparatus and method for simply and correctly loading a donor web wound upon a spool into the printer which prevents operation of the printer when incorrectly loaded.